archive: SETI [ASTRO] Study Associates Asteroid Or Comet Impact With

SETI [ASTRO] Study Associates Asteroid Or Comet Impact With

Larry Klaes ( lklaes@bbn.com )
Thu, 10 Dec 1998 09:09:32 -0500

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>Date: Wed, 9 Dec 1998 20:47:35 GMT
>From: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>To: astro@lists.mindspring.com
>Subject: [ASTRO] Study Associates Asteroid Or Comet Impact With
Extinctions In Argentina
>Sender: owner-astro@brickbat12.mindspring.com
>Reply-To: Ron Baalke <BAALKE@kelvin.jpl.nasa.gov>
>
>
>Embargoed until 4 p.m. EST December 10, 1998
>Contact: Scott Turner, Brown University News Bureau
> 401 863-1862 Scott_Turner@Brown.edu
>
>IMAGE at
>http://www.brown.edu/Administration/News_Bureau/1998-99/98-052g.html
>(upper and lower case in URL may matter)
>
>36 types of animals disappeared 3.3 million years ago
>
>Study associates asteroid or comet impact with extinctions in Argentina
>
>A paper in Science magazine proposes that a major ecosystem-altering
>asteroid or comet impact took place 3.3 million years ago - a
>geologically recent time - in what is now Argentina.
>
>PROVIDENCE, R.I. -- A new study shows that a previously unknown impact
>from an asteroid or comet coincides with the disappearance of 35
>different types of ancient mammals and a flightless bird 3.3 million
>years ago. The impact may have directly caused the regional extinctions
>or triggered a climate change that led to the disappearance of the
>animals in what is now southeastern Argentina.
>
> The findings may provide an opportunity for scientists to study the
>cause and effect of an event that wiped out animal life similar to
>species on Earth today.
>
> "Unlike what impacts did to dinosaurs and other prehistoric
>creatures, this was not an event that led to global extinctions," said
>principal investigator Peter Schultz, professor of geological sciences at
>Brown University and an impact specialist. "We've found something linked to
>much more recent land history. The advantage to studying something this
>young is that you can really examine the forensics.
>
> "This is a threshold event. It may have been small enough to cause
>regional damage and extinctions and may have triggered a climate change. El
>Nino or a volcanic eruption produces small tweaks to the climate compared to
>what one of these impacts can do." The cyclical cooling of the Earth's
>temperatures that began soon after the impact 3.3 million years ago
continues
>today, he said.
>
> The study is published in this week's Science magazine. Its
>co-authors are Argentinean scientists Marcelo Zarate and Cecilia Camilion;
>Willis Hames, an Auburn University geologist; and John King, a researcher in
>the Graduate School of Oceanography at the University of Rhode Island. The
team
>studied an 18-mile-long narrow layer of greenish glass and red brick-like
>materials found in the high ocean cliffs of southeastern Argentina. Called
>escoria, the glass had puzzled scientists since it was first described in
1865.
>
>[Editors: A color image of the escoria is available at the News Bureau's web
>site. The URL is stated above.]
>
> The glass and surrounding red-baked powder bear the signatures of a
>powerful ancient blast archived in the thick Argentine dust, say the
>researchers. They describe a half-dozen physical signs, from the twisted and
>folded shapes of the glass to its isolation from other potential sources
such
>as volcanoes. Chemical analysis of the glass produces all the right impact
>signatures: unusually high levels of magnesium oxide and calcium oxide,
>significant amounts of iridium and chromium, and only the tiniest traces of
>water.
>
> The study shows the glass occurs just below a layer of dusty deposits
>containing fossil evidence of a 3-million-year-old disappearance of 36 local
>types of animals. Extinct species include large armadillo-like creatures,
>ground sloths, hoofed groups of related mammals and a flightless
>carnivorous bird. Other fauna later appeared in their place.
>
> By using a laser fusion technique to measure heavy to light argon
>atoms in the glass, and by comparing the magnetic readings of the glass
>layer to published records of magnetic-field changes over the eons, the
>researchers date the glass as 3.3 million years old, just prior to the
>extinctions.
>
> Using research by other scientists that compared heavy to light
>oxygen isotopes in sediment cores from the nearby ocean floor, Schultz and
>colleagues offer evidence of a sudden drop in both atmospheric and water
>temperatures almost 3.3 million years ago. The finding indicates that
>a climate change occurred shortly after the glass appeared and just
>prior to the animal life turnover.
>
> "This research is analogous to comparing several time clocks," said
>Schultz. "We compared a clock in the glass to a clock in the soil to a clock
>in the deep-sea cores. This told us the conditions at the time. We were
>surprised to find that the appearance of the glasses and the turnover of the
>fauna coincided with a temperature drop."
>
> The research began as a simple project to determine the origin and
>age of the escorias. However, the work identified a series of coincidences
>that strongly suggest a major, ecosystem-altering event took place relatively
>recently, geologically speaking, he said.
>
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